1. Field of the Invention
This application relates generally to a vehicle air brake system, to a multi-function valve and other valves and, in one embodiment, to improvements in a system of the type disclosed and claimed in U.S. Pat. No. 4,685,744 which is commonly assigned with this application.
2. Description of the Prior Art
Parking, emergency and service air brake systems that are presently employed on trucks, trailers, truck tractors, buses and other air-brake equipped vehicles generally include diaphragm brake chambers for all axles, including both non-steerable and steerable axles. The pressure supply systems which are employed in such air brake systems generally comprise compressors and reservoirs along with multiple valves employed for the various operating modes of the brake system. There are generally two separate air systems employed, namely, a service or primary system, and an emergency or secondary system. Not only are the valves numerous, but they vary in complexity of construction. Such valves include service relay valves, spring brake control valves, quick release valves and others. Operationally, treadle valves are commonly used for service brake applications and operated, push-pull valves are used for parking and emergency applications. Further, the power or pressure supply equipment utilize one-way and two-way check valves or other protection valves to protect one air system from another.
The purposes of having two air systems and the rather complex valving arrangements that operate therewith are many. One purpose is to provide safety in the event that there is a complete loss of pressure in one of the systems or at a connection between the tractor and the truck trailer of a motor truck vehicle. A further purpose of such systems is to allow a driver to release and reapply brakes in the event of pressure loss in one side of the system. It is, therefore apparent that safety and back-up operation are important in air brake systems. In fact, federal and state highway safety laws require that air systems meet certain requirements, including not only having a primary/secondary pressure operation, but also with regard to providing braking for emergency and parking operation prior to loss of air pressure.
The system of U.S. Pat. No. 4,685,744 was an improvement upon prior systems of this type in several respects. It includes a brake assembly at each brake actuator rod which contains a single diaphragm chamber. The diaphragm drives the brake actuator rod forward to apply the brakes when a sufficient pressure is supplied to the air receiving inlet side of the chamber. Otherwise a return spring returns the actuator to release the brakes. The input port to the chamber is connected to a two-way, open-center shuttle valve, one input to the valve being connected to the service or primary air supply and the other input to the valve being connected to the emergency or secondary air supply. In the service application, the service supply pressure is increased thereby closing the emergency input side. If there is failure or loss of pressure on either side, but not both, the valve will shut off the low pressure side and operate normally with respect to the remaining pressurized side. The brakes include a rack and emergency piston having a pawl end which engages and holds the actuator in place when there is loss of supply pressure and the brakes have been actuated. Prior to such actuation, an adequate supply of emergency air pressure maintains the pawl end in its disengaged state. After the pawl end is engaged, then a resupply of pressure applied to the emergency side of the shuttle valve and to the piston will relieve the holding pressure between rack and pawl, while lifting the pawl from the rack. In the emergency brake application sequence, the mechanical locking piston is delayed in its fall until air bleeds off the tank or after tank pressure reaches a predetermined level.
In some prior systems, a pressure protection valve on the primary tank prevents air flow until the emergency tank is partially full.
In the U.S. Pat. No. 4,685,744 system, the service line is in communication with both the primary and emergency systems. Thus, in service operation, actuating air pressure is supplied by both tanks.
Another system on the market is the Bendix DD3. This is a double diaphragm, air actuated, mechanically held brake. The mechanical locking brake assembly includes a tapered actuator rod. The DD3 uses roller balls in place of a piston rod. These roller balls are held away from the actuator rod by air until the emergency brake is applied. When applied, the actuator rod is forced forward by a smaller diaphragm to begin applying the brakes while at the same time the air holding the roller ball is exhausted and a spring forces it down onto the actuator rod. The roller balls are designed to move in only one direction. This allows the actuator rod to move forward and apply the brake but prevents the rod from moving backward and releasing the brake.
In order to release the emergency brake, air is applied to the smaller diaphragm as well as the roller ball. Since the Bendix DD3 system releases the emergency brake at the same pressure as was used to apply the brake, an independent foot application is required to release the parking brake. The Bendix DD3 does not time the mechanical locking brake. It applies the brake and engages the roller balls simultaneously. This could lead to early contact between the actuator rod and the roller balls and cause mechanical wear.
There has long been a variety of unrecognized, unaddressed, and/or unsatisfied needs related to brake systems. These needs include a need for:
a system which will reduce brake wear and brake drag by using a peak pressure to release the brakes and a reduced, yet sufficient, air pressure to apply the brakes evenly and gradually; PA1 a system which will reduce stopping distances and increase vehicle stability by providing regulated pressure as desired to achieve uniform pneumatic balance to all brakes; PA1 a system in which, even if one of the air supply lines is completely broken, or one of the reservoirs is ruptured or leaking, the brakes could still be applied; PA1 a system in which there will still be air against a brake diaphragm even if all air reservoirs in the system are emptied and in which the flow lines are protected with one way check valves and an automatically closing port which prevent the unwanted discharge of air on the brakes; PA1 a system in which stepping on a footbrake in a service brake system will effectively result in the disengagement of brake locking mechanism pistons and will relieve all air off an interrelated parking brake system instantaneously; PA1 a system which is easy and safe to work on; PA1 a system in which the number of individual valves and lines is reduced and one multifunction sequence and control valve controls and coordinates tank fillings and brake application; PA1 a system which eliminates the need for an independent foot pedal application for a clean release of the mechanical locking mechanism by utilizing a peak pressure. PA1 a pressure protection valve (in the trailer mode) for insuring that the emergency reservoir is filled first and allows brake release before a service (secondary) tank is filled, or vice versa; PA1 a pressure reduction valve for insuring that air at a desired pressure is applied to the brakes; PA1 an emergency control valve for insuring the system is charged to a certain safe level prior to brake release; in a low pressure mode it insures that the brakes can still be applied at the desired pressure; opens at a higher pressure than that at which it closes, so system air-up is not required each time the brakes are applied at a marginal pressure; PA1 a syncro valve which once brakes are applied, controls the locking pistons of the brakes so they release and are applied at the desired pressure without unnecessary wear or frictional contact with push rod racks; PA1 one-way check valve means for controlling and directing flow to the various other valves and reservoirs; PA1 a bypass valve for allowing air pressure to bleed by the syncro valve to lock the brakes; PA1 a bypass valve to allow a peak pressure to be achieved for brake release; and PA1 inlet ports for receiving compressed air from a compressed air supply and lines or channels through which this air can be controllingly communicated to a compressed air reservoir or reservoirs in an air brake system and to brake assemblies and other valves and apparatuses in the system.